Most motor vehicles are equipped with an internal combustion engine, which generally provides the drive of the vehicle. Such an internal combustion engine, preferably when it is configured as a piston engine, has a crankcase. In the crankcase there is a crankshaft, which is connected via connecting rods to pistons of the individual cylinders of the internal combustion engine. Leaks between the pistons and the associated cylinder walls result in a blow-by gas stream, through which blow-by gas passes from the combustion chambers into the crankcase. To avoid impermissible overpressure in the crankcase, modern internal combustion engines are equipped with a crankcase ventilation device to discharge the blow-by gases from the crankcase. To reduce emissions of pollutants, the blow-by gas is usually fed with the aid of the crankcase ventilation device to a fresh air system of the internal combustion engine, which supplies the combustion chambers of the internal combustion engine with fresh air. There is an oil mist in the crankcase, so the blow-by gas entrains oil. To reduce the oil consumption, a crankcase ventilation device usually has an oil separating device and preferably an oil return, which conducts the separated oil back to the crankcase.
With crankcase ventilation devices, a distinction is drawn between passive systems and active systems. Passive systems use the pressure difference between the crankcase and the vacuum in the fresh air system to drive the blow-by gas. The vacuum in the fresh air system varies greatly depending on the respective operating state of the internal combustion engine. Operating states can also occur in which the available pressure difference is not sufficient to discharge enough blow-by gas. Furthermore, each oil separating device has a flow resistance for the blow-by gas, which makes it more difficult to discharge the blow-by gas. In contrast to this, active systems operate with a conveying device to drive the blow-by gas, so that a sufficient pressure difference can always be provided to discharge the required amount of blow-by gas from the crankcase. Also, the flow resistance of the respective oil separating device can easily be overcome with an active system. However, in active systems the installation outlay is disadvantageous owing to the separate conveying device, since a separate conveying device is associated with correspondingly high costs.
Oil separating devices operate according to various principles. Inertial separators are known, such as cyclone separators, impactors and centrifugal separators, as well as filter devices and electrostatic separation devices. A crankcase ventilation device that operates with an oil separating device configured as an impactor is known for example from WO 2009/080492 A2.